Conventional methods for manufacturing hybrid circuits consist of gluing chips, containing individual electronic function elements, on a substrate, such as a ceramic plate that is layered with strip conductors. An adhesive, such as an epoxy resin mixed with silver, is used to provide a conducting connection between the strip conductors and the chip. In order for the glued connection to conform with the mechanical and electrical requirements of the circuit, an appropriate amount of adhesive must be applied to the substrate and the chip must be slightly pressed down into the adhesive. In such a situation, it is likely that some of the adhesive will be pushed out from underneath the chip, particularly when one is working with very small chips, such as individual LEDs. Undesirable electrical connections are created if the protruding beads of adhesive touch adjacent strip conductors, or if the beads of adhesive touch adjacent chips. To prevent this situation, care must be exercised to ensure that a minimal distance is maintained between adjacent strip conductors, and thus, adjacent chips. Alternatively, the excess adhesive must be removed in a subsequent manufacturing step. In either case, the attainable packing density of the circuit is limited.
Normally, monolithic integration techniques are used for the manufacture of arrays consisting of identical function elements, i.e. a chip produced which contains all function units in the desired sequence and packing density. Electronic memory circuits are typically manufactured in this manner, because it results in high packing densities. However, if monolithic integration is supposed to be justifiable with respect to yield and profitability, one must be able to produce useable function units at a high yield and high packing density.
However, production yields are often too small and unprofitable with respect to the manufacture of chips that require a lot of energy, and thus, a relatively large amount of surface space. In many cases, the materials or the production methods used are simply not suitable to the task. This particularly applies to the manufacture of gallium-arsenide light emitting diode arrays (GaAs-LEDs), which today are usually produced by gluing individual LEDs onto a substrate.
The attainable packing density is a primary concern with present assembly methods. An LED can have a size of approximately, 0.25.times.0.25.times.0.18 mm, for example, and produce a visible wavelength that is detectable by a human eye. When securing elements of such a small size, one must to apply the adhesive to practically the entire surface of the element. Otherwise, it is not possible to ensure that the element will be properly fastened to the substrate. Using present production methods, a portion of the adhesive is laterally pushed out from underneath the LED when the LED is positioned on the substrate, even if the dispensing of the adhesive is satisfactory metered and exactly positioned. Accordingly, the manufacture of LED arrays require a space of as much as twice their bearing surface, unless the pushed out beads of adhesive are removed in additional manufacturing steps. Thus, present state of the art manufacturing techniques only permit the production of LED arrays having a packing grid of approximately 1 mm; i.e., one LED per mm.sup.2.
Since conventional manufacturing techniques result in low packing density LED arrays, wherein only approximately one quarter of the substrate surface forms an effective illuminated surface, images produced by such LED arrays are perceived by the human eye as being coarse, i.e., clearly composed of light dots. Accordingly, it is desirable to be able to manufacture high packing density GaAs-LED arrays in which the image quality of an image displayed by the LED array is increased. Further, it is desirable to be able to produce high resolution, small size displays.